In recent years, from the viewpoint of environmental protection, energy saving, and the like, there is an increasing interest in electric vehicles. Higher rotation speed and downsizing are required of driving motors of the electric vehicles, and accordingly, their driving frequency has become around 800 Hz.
When such a driving motor is in operation, high frequency components several times as high as the driving frequency is superimposed on the driving frequency. This gives rise to a demand that a non-oriented magnetic steel sheet being a core material of the driving motor should be excellent not only in mechanical property enabling the higher rotation speed and downsizing but also in magnetic property, especially, in core loss property, in a high-frequency range of 400 Hz to 2 kHz.
The core loss can be roughly classified into eddy-current loss and hysteresis loss. The eddy-current loss is proportional to the square of a thickness of the non-oriented magnetic steel sheet and is in inverse proportion to specific resistance. Therefore, in order to reduce the eddy-current loss, an attempt has been made to reduce the thickness of the non-oriented magnetic steel sheet. Another attempt has been made to increase a Si amount and/or an Al amount in the non-oriented magnetic steel sheet to increase the specific resistance. The increase in the Si amount and/or the Al amount can also increase mechanical strength (rotor rigidity).
However, related arts cannot fully reduce the core loss in the high-frequency range of, for example, 400 Hz to 2 kHz.